moved out static pre processor stuff to a util class, as it will be used by REPL. Later we may want to do it by inheritance, but for now it's good enough
added filepreprocessor to process #r and #load in REPL
fixed tests that wouldn't compile
added support for adding references during REPL runtime
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into 221
added REPL #load and #r tests, and refactored #load and #r check from ExecuteReplCommand to Repl Execute
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into 221

Conflicts:
	src/ScriptCs.Engine.Roslyn/RoslynScriptEngine.cs
Merge pull request #236 from filipw/221

added support for #load and #r in REPL